The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
To reduce the quantity of undesirable particulate matter and nitrogen oxides (NOx) emitted to the atmosphere during internal combustion engine operation, a number of exhaust aftertreatment systems have been developed. A need for exhaust aftertreatment systems particularly may arise when diesel combustion processes are implemented.
One method used to reduce NOx emissions from internal combustion engines is known as selective catalytic reduction (SCR). SCR may include injecting a diesel exhaust fluid (DEF), such as urea, into the exhaust stream of the engine to form a DEF and exhaust gas mixture that is subsequently passed through a reactor containing an SCR catalyst. The SCR catalyst is configured to reduce the NOx concentration in the presence of the ammonia from the DEF. For example only, the SCR catalyst may include activated carbon or metals, such as platinum, vanadium, or tungsten.